Within the field of pallet transfer, there exists a need for accurate and efficient location of moving pallets on a transfer mechanism. Such pallets may be employed as holding means for devices being constructed along an assembly line type of operation. For example, a device may be placed on a pallet moving along a transfer mechanism between numerous workstations. At each work station the device being held by the pallet receives discrete attention such as further assembly or testing.
In many cases, the efficiency of pallet transfer operations is highly dependent on movement of a high volume of pallets and associated devices during certain definable cycles. Typical operations may depend on assembly of tens of thousands of units during one week's time. Frequently such systems include workstations which are synchronously related, e.g., with efficiency dependent upon output of other workstations. Accordingly, synchronous operations are subject to systemwide inefficiencies when virtually any work station experiences difficulty or breakdown. Inefficiencies of merely a few seconds in time, or less, may result in substantial delays when such inefficiencies are multiplied many thousands of times as each device or unit experiences such delay. Thus, it is preferable to design assembly line pallet transfer systems utilizing a non-synchronous mode of operation.
Further delays in prior art pallet transfer systems are likely when pallets are being positioned at a workstation just prior to receiving a workstation function. Specifically, pallets which are not consistently precisely located relative to a workstation require workstation tooling with broader tolerances. Such lack of precision frequently results in timing delays and equipment wear. It is also common in such systems to employ relatively complex mechanical machinery to achieve proper alignment and positioning of a pallet.
One example of a machine for transferring pallets along a transfer mechanism is disclosed in U.S Pat. No. 3,646,656 issued Mar. 7, 1972, to Zilahy et al. The Zilahy et al patent discloses moveable carriers suspended on vertical rails in a cantilever relationship for support of the pallets. The carriers move on a continuous chain between workstations. The chain has wear plates which engage and frictionally drive the carriers until a mechanical brake mechanism disengages the carrier from the chain. Pallets which are mounted on top of the carriers are roughly positioned at various workstations and then more accurately located by spring loaded dual-acting arms which laterally move the pallets across the top surface of the carriers into a wedge-shaped member substantially opposite the spring loaded arms. Considerable mechanical inefficiencies are apparent in the Zilahy et al system due to the number of complex moving parts and the distances required for the pallet to be moved at workstations.
A different pallet transfer system which has been used by Honeywell Inc. in assembly operations includes a static roller system for synchronous movement of pallets through various workstations, with pallets transported between workstations on a belt conveyor device. At appropriate workstations, a metering system roughly locates standard width pallets, thus permitting a precise locating arm to engage each of the pallets in momentary locking and positioning relationship. Although the prior Honeywell system is preferable and advantageous over any other known synchronous system, the present invention permits even greater mechanical and timing efficiencies, as will be shown in the accompanying specification, claims, and drawings. Also, prior art problems experienced in systems such as Zilahy and the Honeywell system include jamming of engaging bars against misaligned pallets.
What has been needed, therefore, is a system for very precise and rapid locating of pallets positioned at a workstation along a moving pallet transfer mechanism. What has been further needed is a very precise pallet transfer and locating system which is mechanically efficient in operation as well as being non-synchronous so as to prevent systemwide inefficiencies.
What has been further needed is a pallet having a sidewall comprising an arcuate surface for cooperating with a curved guide rail at a corner portion of a pallet transfer mechanism in order to transfer the pallet around the corner portion of the transfer mechanism while maintaining the orientation of the pallet with respect to the direction of pallet transfer.
What has been further needed is a method to very precisely locate and transfer moving pallets from a moving transfer mechanism to permit efficient and accurate machining and other operations on devices located on the pallets.